1. Field of the Invention
The present invention relates to a fuel cell using liquid fuel as fuel and used particularly in electronic equipment, and the like.
2. Description of the Related Art
Recently, various types of equipment such as OA equipment, audio equipment, and radio equipment are reduced in size due to development of a semiconductor technology, and it is further required to be provided with portability. To satisfy the requirement, a primary cell, a secondary cell, and the like, which are available easily, are used. However, the operating time of the primary and secondary cells is limited in their function, and thus the operating time of the OA equipment or the like using them is naturally limited.
When the primary cell is used, the OA equipment or the like can be operated by replacing the cell after the discharge thereof is finished. However, since the operating time of the primary cell is short with respect to its weight, it is not suitable for portable equipment. Further, although the secondary cell can be recharged after the discharge thereof is finished, the cell is disadvantageous in that not only a place where it is used is limited because a power supply for recharging it is necessary, but also a considerable time is necessary to recharge it. In particular, in OA equipment or the like to which the secondary cell is assembled, the operating time of the equipment cannot help being limited because it is difficult to replace the cell even if the discharge thereof is finished. Since it is difficult to operate various small equipment by a prolongation of the conventional primary is and secondary cells as described above, there is required a cell suitable for a long time operation.
As means for solving the above problem, recently, attention is paid to a fuel cell. The fuel cell has an advantage in that not only it can generate power only by being supplied with fuel and an oxidizer but also it can continuously generate power by replacing only fuel. Accordingly, it can be said that the fuel cell is a system which is very advantageous to operate small equipment such as OA equipment whose power consumption is small if the size thereof can be reduced. In particular, a fuel cell, which uses hydro carbon liquid such as alcohol as fuel, can safely carry fuel having an high energy density, it is hopeful as a fuel cell for electronic equipment.
The fuel cell described above has the following problems. That is, when liquid fuel is used in a fuel cell for electronic equipment, the electronic equipment fails if the liquid fuel and moisture leak from the fuel cell. In particular, in a fuel cell such as a fuel cell for portable equipment, which operates at a relatively low temperature, an electrolyte membrane, which exhibits proton conductivity in a water containing state as electrolyte, is often used due to the high ion conductivity thereof. Further, in a fuel cell, an electrolyte membrane is sealed by being clamped between seal members to prevent fuel, which is generally an active substance, from being mixed with air or from leaking to the outside. However, in this state, the end surface of the electrolyte membrane is exposed to outside air, from which a problem arises in that water in the electrolyte membrane emits as moisture from the end surface and adversely affects the electronic equipment.
For example, in a fuel cell 100 shown in FIG. 5, a membrane electrode assembly 104 is formed by clamping an electrolyte membrane 103 between a fuel electrode 101 and an oxidizer electrode 102 with its outer periphery 103a exposed therefrom. A unit cell is formed by clamping the membrane electrode assembly 104 between two separators 105 and 106. In the fuel cell 100 arranged as described above, a leakage of liquid fuel and air to the outside is prevented by clamping seals between the separators 105 and 106 and the protruding portion 103a of the electrolyte membrane 103. However, since the protruding portion 103a of the electrolyte membrane 103 is exposed to outside air, water in the electrolyte membrane 103 leaks to the outside as moisture.